1. Field of the Invention
The present invention relates to a thinner composition and to a method of stripping a photoresist using the same.
2. Description of the Related Art
In order to fabricate semiconductor devices, it is necessary to accurately inject impurities into specific minute regions of a silicon substrate. These minute regions are typically inter-connected to form devices in very large scale integrated (VLSI) circuits. Patterns which define the minute regions are formed by photolithography processes. Generally, in photolithography, a photoresist polymer film is coated on a substrate, and then, the polymer film is selectively developed by exposure to ultraviolet rays, electronic rays or X-rays. The developed portions of the photoresist are removed, and the remaining non-developed photoresist polymer film pattern functions to mask selected areas of the underlying substrate during subsequent processes.
Rework and edge bead removal (EBR) processes are common processes encountered during photolithography of semiconductor wafers or substrates.
Occasionally, the photolithography process suffers a process failure in which the photoresist is not properly coated or patterned on the substrate. When a process failure occurs, the rework process is carried out where the photoresist film coated on the substrate is completely removed using a stripping composition, and then, the substrate is re-used.
On the other hand, EBR results from certain characteristics of the photoresist coating process. That is, the photoresist is coated onto a wafer by dispensing the photoresist material onto a surface of the wafer while the wafer is rotating. As a result, the photoresist material tends to accumulate at the edge of the wafer, forming a so-called edge bead. Also, during the spraying process, photoresist material inevitably becomes coated onto the backside of the wafer. Accordingly, in the EBR process, a stripper composition is used to remove any unwanted photoresist from the edge and backside of the wafer.
During both the rework and EBR process, it is important that the photoresist not dissolve too slowly or incompletely in the stripper composition, otherwise residual contaminants (photoresist) may remain on the substrate after the stripping process. Any such contaminants can reduce device yield and adversely impact product reliability.
In the meantime, to accommodate for increased degrees of integration of semiconductor devices, new photoresist are being developed. For example, a photoresist having novolak resin as a main component has been developed for application with light of I-line or G-line wavelengths. Also, amplified type photoresists which respond to an excimer laser or deep ultraviolet (DUV) also have been employed.
Examples of the thinner compositions that can be used to dissolve various kind of photoresist are disclosed in commonly assigned U.S. Pat. No. 5,866,305 (issued to Chon et. al.), commonly assigned U.S. Pat. No. 6,159,646 (issued to Jeon et. al.), and commonly assigned U.S. Pat. No. 6,458,518 (issued to Sang-sik Moon et al.)
In the U.S. Pat. No. 5,866,305, thinner compositions are disclosed which include ethyl lactate and ethyl-3-ethoxy propionate, or ethyl lactate, ethyl-3-ethoxy propionate and gamma-butyro lactone. These thinner compositions are commonly used in semiconductor device fabrication, but are very expensive due to the high price of ethyl 3-ethoxy propionate. Further, the thinner compositions cannot sufficiently dissolve certain types of photoresists, for example, amplified type photoresists. Likewise, in the U.S. Pat. No. 6,159,646, a thinner composition including ethyl-3-ethoxy propionate, ethyl lactate and gamma-butyro lactone is disclosed. Again, however, the use of ethyl 3-ethoxy propionate results in high costs.
The U.S. Pat. No. 6,458,518 discloses a thinner composition for stripping a photoresist which includes acetone, gamma-butyro lactone and an ester compound. The acetone exhibits a strong penetration characteristic which results in a poor edge profile characteristic of the thinner composition, which is clearly evident when the thinner composition is used to dissolve a deep ultraviolet (DUV) resist layer. In addition, the acetone is so volatile that when the thinner composition used, photoresist residues often remain, especially when the EBR process is carried out using a thinner composition made up of N-Butyl Acetate (hereinafter, referred to as NBA), gamma-butyro lactone (GBL), and acetone.
The above-described thinner compositions are commonly used in both the rework process and the EBR process, but do not strip the photoresist layer to the same extent in both of the processes. Accordingly, there is a demand for photoresist stripper compositions which exhibit favorable stripping characteristics in both the rework and EBR processes, and with respect to different types of photoresists, yet which can be manufactured at relatively low cost.
According to a first aspect of the present invention, there is provided a thinner composition for stripping a photoresist, where the thinner composition includes propylene glycol mono-methyl ether acetate (PGMEA), ethyl 3-ethoxy propionate (EEP), and xcex3-butyro lactone (GBL).
According to another aspect of the present invention, there is provided a thinner composition for stripping a photoresist, where the thinner composition includes propylene glycol mono-methyl ether acetate (PGMEA), ethyl 3-ethoxy propionate (EEP), and propylene glycol mono-methyl ether (PGME).
According to yet another aspect of the present invention, there is provided a method of stripping a photoresist layer, where the method includes providing a thinner composition which includes propylene glycol mono-methyl ether acetate (PGMEA), ethyl 3-ethoxy propionate (EEP), and at least one of xcex3-butyrolactone (GBL) and propylene glycol mono-methyl ether (PGME), stripping a photoresist layer coated on at least one of a backside and an edge portion of a substrate by bringing the thinner composition into contact with the photoresist layer, and drying the thinner composition that is brought into contact on the photoresist layer.
According to still another aspect of the present invention, there is provided a method of stripping a photoresist layer, where the method includes providing a thinner composition which includes propylene glycol mono-methyl ether acetate (PGMEA), ethyl 3-ethoxy propionate (EEP), and at least one of xcex3-butyrolactone (GBL) and propylene glycol mono-methyl ether (PGME), spraying the thinner composition onto a substrate coated with a photoresist layer while the substrate is rotated at a first speed, and drying the thinner composition that is brought into contact on the substrate.
According to the present invention, a relatively inexpensive compound, i.e., propylene glycol mono-methyl ether acetate (PGMEA), is used as a major component of the thinner compositions. However, while costs are substantially reduced in this manner, the thinner compositions exhibit very favorable photoresist stripping characteristics. Also advantageous is the eco-friendly nature of the compounds of the thinner compositions of the present invention.